U.S. patent application number 12/602721 was filed with the patent office on 2010-07-08 for providing space division multiple access in a wireless network.
Invention is credited to Peter M. Deane, Xiao-Dong Li, Patrick Lie Chin Cheong, Neil McGowan, Jia Ming.
Application Number | 20100173639 12/602721 |
Document ID | / |
Family ID | 40468505 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100173639 |
Kind Code |
A1 |
Li; Xiao-Dong ; et
al. |
July 8, 2010 |
PROVIDING SPACE DIVISION MULTIPLE ACCESS IN A WIRELESS NETWORK
Abstract
To provide space division multiple access in a wireless network,
plural beams are transmitted within a cell segment. Different
information sets are sent in the corresponding plural beams, where
one or more of the information sets are detectable by a mobile
station depending upon a location of the mobile station in the cell
segment. An indication responsive to which of the different
information sets is detected by the mobile station is received, and
beam selection from among the plural beams is performed according
to the received indication.
Inventors: |
Li; Xiao-Dong; (Ottawa,
CA) ; Deane; Peter M.; (Fitzoy Harbour, CA) ;
Lie Chin Cheong; Patrick; (Kanata, CA) ; McGowan;
Neil; (Stittsville, CA) ; Ming; Jia; (Ottawa,
CA) |
Correspondence
Address: |
TROP, PRUNER & HU, P.C.
1616 S. VOSS ROAD, SUITE 750
HOUSTON
TX
77057-2631
US
|
Family ID: |
40468505 |
Appl. No.: |
12/602721 |
Filed: |
July 16, 2008 |
PCT Filed: |
July 16, 2008 |
PCT NO: |
PCT/IB2008/003365 |
371 Date: |
December 2, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60950007 |
Jul 16, 2007 |
|
|
|
Current U.S.
Class: |
455/450 ;
455/562.1 |
Current CPC
Class: |
H04B 7/0639 20130101;
H04B 7/063 20130101; H04B 7/0695 20130101; H04B 7/061 20130101;
H04B 7/0697 20130101; H04W 74/00 20130101; H04B 7/0632 20130101;
H04B 7/088 20130101 |
Class at
Publication: |
455/450 ;
455/562.1 |
International
Class: |
H04W 72/00 20090101
H04W072/00; H04W 88/08 20090101 H04W088/08 |
Claims
1. A method of providing space division multiple access in a
wireless network, comprising: transmitting plural beams within a
cell segment; sending different information sets in the
corresponding plural beams, wherein one or more of the information
sets are detectable by a mobile station depending upon a location
of the mobile station in the cell segment; receiving an indication
responsive to which of the different information sets is detected
by the mobile station; and performing beam selection from among the
plural beams according to the received indication.
2. The method of claim 1, where receiving the indication comprises:
receiving a first indication if a first of the information sets but
not a second of the information sets is detected by the mobile
station; receiving a second indication if the second information
set but not the first information set is detected by the mobile
station; and receiving a third indication if both the first and
second sets are detected by the mobile station.
3. The method of claim 1, wherein receiving the indication
comprises receiving a precoding matrix index.
4. The method of claim 1, wherein the transmitting, sending,
receiving, and performing are performed by a base station in a Long
Term Evolution (LTE) wireless network.
5. The method of claim 1, further comprising: receiving, from the
mobile station, one or more signal quality metrics associated with
the corresponding plural beams, wherein performing the beam
selection is also according to the one or more signal quality
metrics.
6. The method of claim 5, wherein receiving the one or more signal
quality metrics comprises receiving one or more channel quality
indications (CQIs).
7. The method of claim 1, wherein sending the different information
sets comprises sending different reference signal structures,
wherein each of the different reference signal structures has a
same set of pilots.
8. The method of claim 7, wherein the different reference signal
structures employ different phases for at least one pilot of the
sets of pilots.
9. The method of claim 1, wherein performing the beam selection
comprises performing downlink beam selection, the method further
comprising: receiving, by a base station, reference signals from
the mobile station; and determining, based on the reference signals
by the base station, a beam from among the plural beams to
communicate uplink data.
10. The method of claim 1, further comprising: receiving rank
information to indicate a number of layers supportable by a
wireless channel; and selecting a mode of operation based on the
indication and rank information.
11. The method of claim 10, wherein selecting the mode comprises
selecting from among a single input multiple output (SIMO) mode, a
diversity mode, and a multiple input multiple output (MIMO)
mode.
12. The method of claim 1, further comprising: sending a message to
the mobile station, wherein the message indicates an amount of
cyclic shift to apply to a demodulation reference signal; and
receiving the demodulation reference signal from the mobile station
having the amount of cyclic shift applied.
13. The method of claim 12, wherein the amount of cyclic shift
applied is none, the method further comprising: sending a second
message to a second mobile station, wherein the second message
indicates a non-zero cyclic shift to be applied to a demodulation
reference signal sent by the second mobile station.
14. A base station comprising: an antenna assembly to generate
plural beams to be communicated in a cell segment; and a processor
to: transmit different information sets in respective beams to a
mobile station in the cell sector, wherein the mobile station is
able to detect one or more of the information sets depending upon a
location of the mobile station in the cell sector; receive an
indication responsive to which of the different information sets is
detected by the mobile station; and select one or more beams from
among the plural beams according to the received indication for
communicating downlink data to the mobile station.
15. The base station of claim 14, wherein the processor is to
further: receive rank information and beam quality metrics from the
mobile station; and select a mode from among plural modes for
communicating the downlink data.
16. The base station of claim 15, wherein the selected mode is one
of a single input multiple output (HMO) mode, diversity mode, and
multiple input multiple output (MIMO) mode.
17. The base station of claim 14, wherein the processor is to
further: receive a sounding reference signal from the mobile
station; and determine which of the plural beams to use for
communication of uplink data based on the received sounding
reference signal.
18. The base station of claim 14, wherein the processor is to
communicate certain control signals to the mobile station in
diversity mode.
19. An article comprising at least one computer-readable storage
medium containing instructions that when executed by a base station
cause the base station to: cause transmission of plural beams
within a cell segment; send different information sets in the
corresponding plural beams, wherein one or more of the information
sets are detectable by a mobile station depending upon a location
of the mobile station in the cell segment; receive an indication
responsive to which of the different information sets is detected
by the mobile station; and perform beam selection from among the
plural beams according to the received indication.
20. The article of claim 19, wherein the instructions when executed
cause the base station to further select a mode for communicating
data, wherein the selected mode is one of a single input multiple
output (HMO) mode, diversity mode, and multiple input multiple
output (MIMO) mode.
Description
TECHNICAL FIELD
[0001] The invention relates generally to providing space division
multiple access (SDMA) in a wireless network.
BACKGROUND
[0002] Various wireless access technologies have been proposed or
implemented to enable mobile stations to perform communications
with other mobile stations or with wired terminals coupled to wired
networks. Examples of wireless access technologies include GSM
(Global System for Mobile communications) or UMTS (Universal Mobile
Telecommunications System) technologies, defined by the Third
Generation Partnership Project (3GPP); CDMA 2000 (Code Division
Multiple Access 2000) technologies, defined by 3GPP2; or other
wireless access technologies.
[0003] As part of the continuing evolution of wireless access
technologies to improve spectral efficiency, to improve services,
to lower costs, and so forth, new standards have been proposed. One
such new standard is the Long Term Evolution (LTE) standard from
3GPP, which seeks to enhance the UMTS wireless network.
[0004] The 3GPP LTE standards have not yet developed efficient
space division multiple access (SDMA) solutions. SDMA refers to a
technique in which radio frequency (RF) resources (e.g.,
frequencies, time slots, etc.) can be reused in different
geographic regions by transmitting different beams into the
different geographic regions using multi-beam antennas. Because of
inadequate SDMA solutions in the LTE standards, efficiencies
associated with SDMA are not available in conventional LTE wireless
networks.
SUMMARY OF THE INVENTION
[0005] In general, according to a preferred embodiment, a method of
providing space division multiple access in a wireless network
includes transmitting plural beams within a cell segment, and
sending different information sets in the corresponding plural
beams, where one or both of the information sets are detectable by
a mobile station depending upon a location of the mobile station.
Beam selection is performed from among the plural beams according
to the received indication that is responsive to which of the
plural information sets is detected by the mobile station.
[0006] Other or alternative features will become apparent from the
following description, from the drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a block diagram of a communications network that
includes a wireless network in which a space division multiple
access (SDMA) technology is implemented, according to a preferred
embodiment.
[0008] FIG. 2 illustrates an exemplary codebook containing
codewords for encoding signals in corresponding beams of the
wireless network, according to a preferred embodiment.
[0009] FIGS. 3A-3B illustrate exemplary reference signal structures
that each contains pilots coded according to different precoding
matrix index values, according to a preferred embodiment.
[0010] FIG. 4 is a flow diagram of a process of performing downlink
beam selection according to a preferred embodiment.
[0011] FIG. 5 is a flow diagram of a process of performing uplink
beam selection according to a preferred embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0012] In the following description, numerous details are set forth
to provide an understanding of some embodiments. However, it will
be understood by those skilled in the art that some embodiments may
be practiced without these details and that numerous variations or
modifications from the described embodiments may be possible.
[0013] FIG. 1 shows an exemplary wireless network in which a
spatial division multiple access (SDMA) mechanism according to
preferred embodiments is provided. The wireless network includes a
base station 100 that includes an antenna array or other assembly
(multi-beam antenna) 102 for producing multiple beams (spatial
beams) 104, 106 in a corresponding cell sector 108. Although just
two beams 104 and 106 are depicted in FIG. 1, it is noted that more
than two beams can be provided in a cell sector in other
embodiments. SDMA enables radio frequency (RF) resources (e.g.,
frequencies, time slots, etc.) to be reused in different geographic
regions of a cell sector by transmitting different beams into the
different geographic regions using multi-beam antennas. A "beam"
(or "spatial beam") refers to a wireless signal (or wireless
signals) that is (are) transmitted along a particular geographic
path. A beam pattern refers to the coverage area of the beam.
[0014] A cell sector is one section of a cell of a cellular
network. In alternative implementations, rather than providing
multiple beams in a cell sector, it is noted that multiple beams
can be provided in a cell. As used here, a "cell segment" can refer
to either a cell sector or a cell. To provide SDMA, multiple beams
are generated in such a cell segment.
[0015] Although just one base station is depicted in FIG. 1, it is
noted that a wireless network would typically include multiple base
stations. In some implementations, the wireless network is a Long
Term Evolution (LTE) wireless network as defined by the Third
Generation Partnership Project (3GPP). In alternative
implementations, other types of wireless networks can be employed.
Note that reference to a "LTE wireless network" refers to a
wireless network defined by current standards for LTE, or by
subsequent standards that evolve from LTE. Moreover, even though
reference is made to LTE wireless networks in the ensuing
discussion, it is noted that techniques according to preferred
embodiments can also be applied to non-LTE wireless networks.
[0016] A mobile station 110 can communicate using one or both of
the beams 104, 106 in the cell sector 108, depending upon the
position of the mobile station 110 in the cell sector. As depicted,
the mobile station 110 is in a position to communicate using beam
106. The mobile station 110 can move to another location in the
cell sector 108 to communicate using beam 104. Alternatively, the
mobile station 110 can move to a location that is in an overlap
region 105 between the beams 104 and 106, in which case the mobile
station 110 is able to communicate using both beams 104 and
106.
[0017] In an LTE wireless network, the base station 100 includes an
enhanced node B, which includes a base transceiver station that
includes the antenna array 102. The base station 100 also includes
a radio network controller that cooperates with the enhanced node
B. The radio network controller and/or enhanced node B can perform
one or more of the following tasks: radio resource management,
mobility management for managing mobility of mobile stations,
routing of traffic, and so forth. Note that one radio network
controller can access multiple node Bs, or alternatively, a node B
can be accessed by more than one radio access controller.
[0018] As depicted in FIG. 1, the base station 100 includes one or
more central processing units (CPUs) 122, which is (are) connected
to storage 124. Moreover, the base station includes software 126
that is executable on the CPU(s) 122 to perform tasks of the base
station 100, including tasks according to preferred embodiments to
enable support for SDMA in the LTE wireless network.
[0019] The base station 100 is connected to a serving and/or packet
data network (PDN) gateway 112, which terminates the user plane
interface toward the enhanced node B and assumes the responsibility
for package routing and transfer towards an external network 114,
which can be a packet data network such as the Internet or other
type of network.
[0020] The arrangement depicted in FIG. 1 is provided for purposes
of example. In other implementations, other wireless network
arrangements are used.
[0021] In accordance with preferred embodiments, to enable downlink
beam selection, the base station 100 is able to send different
information sets on corresponding beams (e.g., 104, 106) in the
cell sector 108 for receipt by mobile stations within the cell
sector 108. Downlink beam selection refers to selection of one of
the beams 104, 106 (or both beams 104, 106) depending upon the
location of the mobile station to perform communication of downlink
data (from the base station 100 to the mobile station). The
downlink beam selection for a particular mobile station (e.g., 110)
is performed at the base station 100 in response to indications
received from the particular mobile station, where the indications
are generated by the particular mobile station depending upon which
of the information sets was received by the mobile station.
[0022] For example, the mobile station 110 located in a region
corresponding to beam 106 would receive the information set
transmitted in beam 106, but will not receive the information set
transmitted in beam 104. On the other hand, a mobile station
located in a region corresponding to beam 104 would receive the
information set communicated in beam 104, but would not receive the
information set communicated in beam 106. A mobile station located
in an overlap region 105 between the beams 104 and 106 would be
able to receive both information sets communicated in beams 104,
106.
[0023] Depending on the information set(s) detected by the mobile
station, the mobile station will send back a corresponding
indication to the base station 100. The indication sent by the
mobile station will differ depending on which of the information
set(s) is detected by the mobile station. Based on the indication
received from the mobile station, the base station 100 performs
beam selection from among plural beams for communicating downlink
data to the mobile station. The indication received by the base
station 100 from the mobile station enables the base station 100 to
identify the beam that the mobile station is able to receive in the
downlink direction.
[0024] According to preferred embodiments, the SDMA operation
supported by the LTE wireless network is transparent to the mobile
station. In other words, changes do not have to be made to mobile
stations in the LTE wireless network to provide SDMA support, which
reduces costs associated with deploying SDMA. The mobile station is
able to detect the information sets communicated by the base
station--however, the mobile station does not have to recognize
that the information sets were sent in different beams, and the
mobile station does not have to be configured to identify which
beam the mobile station is communicating with.
[0025] In preferred embodiments, the information sets communicated
in the beams 104, 106 include reference signal structures that
contain pilot (reference) signals that are coded according to a
predetermined coding scheme. A pilot (reference) signal is a signal
that is transmitted by the base station and is used by a mobile
station to acquire the wireless network system and to perform other
tasks. In some embodiments, the predetermined coding scheme
involves the use of a codebook that has a number of entries
containing corresponding codewords that can be selectively used for
coding the pilot signals in a reference signal structure.
[0026] In some implementations, each information set communicated
in each of the beams 104, 106 includes all pilot signals of the
cell sector 108. Thus, for example, if the base station 100
transmits two pilot signals in the cell sector 108, then both pilot
signals would be communicated in each information set communicated
in each corresponding beam 104, 106. However, different codings
(using different codewords of the codebook) are applied to the
pilot signals in the different information sets, such that a mobile
station in a region corresponding to beam 104 would receive an
information set containing pilot signals subjected to a first
coding (using a first codeword), while a mobile station in a region
corresponding to beam 106 would receive an information set with
pilot signals subjected to a second, different coding (using a
second codeword).
[0027] FIG. 2 shows an exemplary codebook that has a number of
entries containing exemplary codewords. The codebook is arranged as
a matrix having rows corresponding to four codebook indexes (0, 1,
2, 3), and two columns corresponding to two ranks (1, 2). The
arrangement of FIG. 2 is provided for purposes of example, as the
actual data structure of the codebook may be different. There are
four entries (containing four respective codewords) corresponding
to rank 1 and three entries (containing three respective codewords)
corresponding to rank 2. "Rank 2" indicates that a particular
wireless channel used to communicate data between a base station
and a mobile station is able to use two layers, which means that
the current RF channel between the base station and the particular
mobile station can support two layers (and in a preferred
implementation) these two layers will utilize both beams 104, 106
simultaneously. This simultaneous transmission of data to the
mobile station means that the throughput of data communication is
doubled. On the other hand, "rank 1" means that just a single layer
can be used for the wireless channel that communicates data between
the base station and mobile station. If just a single layer is
enabled, then the data transmitted to a mobile station is
transmitted in just one of the beams 104, 106. Note that rank 2 is
possible when a mobile station is located in an overlap region,
such as overlap region 105, between multiple beams (e.g., 104,
106).
[0028] The entry in the codebook identified by codebook index 0 and
rank 1 has the following value,
1 2 [ 1 1 ] , ##EQU00001##
which means that a first pilot signal and second pilot signal are
transmitted in the same positive phase (corresponding to the "+1"
value).
[0029] On the other hand, the codeword contained in the entry of
the codebook identified by codebook index 1 and rank 1 has
value
1 2 [ 1 - 1 ] , ##EQU00002##
which means that the first pilot signal has positive phase while
the second pilot signal has negative phase (which correspond to the
"+1" and "-1" values, respectively, of the codeword).
[0030] The codeword corresponding to the entry associated with
codebook index 2 and rank 1 has value
1 2 [ 1 j ] , ##EQU00003##
which means that the first pilot signal has positive phase
(corresponding to the "+1" value), while the second pilot signal is
out of phase by 90 degrees (corresponding to the "j" value).
[0031] The codewords associated with the rank 2 entries in the
codebook are interpreted similarly, except that the pilot signals
subjected to rank 2 coding are communicated over two beams, rather
than just one beam as with pilot signals subjected to rank 1
coding.
[0032] FIGS. 3A-3B depict two different information sets, in the
form of reference signal structures 300 and 302, that are
communicated over different beams (e.g., 104, 106). The horizontal
axis of each of the reference signal structures 300, 302 represent
time slots, whereas the vertical axis of each of the reference
signal structures 300, 302 represent subcarriers (at different
frequencies). FIG. 3A shows a reference signal structure in which
the coding applied to pilot signals (represented as R0 and R1) are
subjected to coding applied by the codeword contained in the
codebook entry corresponding to codebook index 0 and rank 1. FIG.
3B shows a reference signal structure in which the coding applied
to pilot signals (represented as R0 and RI) are subjected to coding
applied by the codeword contained in the codebook entry
corresponding to codebook index 1 and rank 1.
[0033] The reference signal structures 300 and 302 differ in that
pilot signal R1 in reference signal structure 300 has a +1 phase
(according to the codeword at codebook index 0, rank 1), while
pilot signal RI in reference signal structure 302 has a -1 phase
(according to the codeword at codebook index 1, rank 1). The R0
pilot signal occupies the same positions in both reference signal
structures 300 and 302, and the R0 pilot signal has the same +1
phase in both reference signal structures 300, 302. However, the R1
pilot signals occupy the same positions in the reference signal
structures 300 and 302, but are out of phase by 180.degree. in the
reference signal structures 300 and 302.
[0034] The indication that is reported by the mobile station back
to the base station 100 depends upon which reference signal
structure is detected by the mobile station. In other words, if a
first information set is detected by the mobile station, then a
first indication is sent. However, if a second information set is
detected by the mobile station, then a second indication is sent.
If a combination of the first and second information sets (e.g.,
reference signal structures corresponding to either beam 1 or beam
2) are received by the mobile station, then depending on the
relative strength of the two sets, either the beam corresponding to
the stronger set will be indicated by the mobile station or if the
signals are of comparable strength then a third indication may
result that does not correspond to either beam.
[0035] In some preferred embodiments, the indication reported by
the mobile station is a precoding matrix index (PMI). In an
exemplary implementation, a mobile station that is exclusively in a
region corresponding to beam 1, with no significant interference
from beam 2, will report a first PMI, such as
[ 1 1 ] , ##EQU00004##
which corresponds to the codeword at codebook index 0, rank 1. On
the other hand, a mobile station that is located exclusively in
beam 2 (with no significant interference from beam 1) will report
the second PMI, such as
[ 1 - 1 ] , ##EQU00005##
which corresponds to the codeword at codebook index 1, rank 1. In
some cases, the mobile station can report another rank 1 PMI, such
as
[ 1 j ] or [ 1 - j ] . ##EQU00006##
If such other rank 1 PMI is reported, then that indicates that the
mobile station can see more than one beam. In this scenario, a
diversity mode is employed in which the same data is multiplexed
using both beams (employing either time diversity, space diversity,
block code diversity or some combination of these methods) to the
mobile station. In one implementation, the diversity mode used is a
spatial frequency block coding (SFBC) mode. A mobile station can
see both beams if the mobile station is in an overlap region (e.g.,
105 in FIG. 1) between the two beams.
[0036] If the mobile station detects that an RF channel can support
two layers, and if the mobile station is in the overlap region
(e.g., 105) between two beams, then the mobile station can report a
rank 2 PMI, such as PMIs corresponding to one of the codewords
depicted in the codebook of FIG. 2. In such a scenario, the base
station will use a MIMO (multiple input multiple output) mode, in
which both beams are used for simultaneously communicating
different data to the mobile station, to improve throughput.
[0037] FIG. 4 is a message flow diagram of a procedure to perform
downlink beam selection by the base station 100. The base station
transmits (at 402) reference signal structures in corresponding
beams in a given cell sector. Depending on where the mobile station
is located, the mobile station can receive one of the beams, or the
other of the beams, or both of the beams (assuming that there are
two beams). Note that in alternative implementations, more than two
beams can be transmitted by the base station.
[0038] Based on the reference signal structures detected by the
mobile station, the mobile station sends (at 404) a PMI back to the
base station 100. Note that the mobile station can also send other
information back to the base station, where such other information
can include metrics representing beam quality. For example, a
metric representing beam quality can be in the form of a channel
quality indicator (CQI). The other information transmitted by the
mobile station back to the base station can also include rank
information (e.g., rank 1 or rank 2) to indicate the number of
layers supported by an RF channel over which the mobile station is
communicating. The PMI, CQI, and rank information can be sent by
the mobile station to the base station 100 in one control message,
or in plural control messages. For example, the PMI, CQI, and rank
information can be communicated in a physical uplink control
channel (PUCCH), or in some other control channel.
[0039] Based on the received PMI and other information, the base
station 100 can perform (at 406) downlink beam selection. Beam
selection can include the base station selecting one of the beams,
or the other of the beams, or both beams, for communicating
downlink data with the mobile station. The PMI informs the base
station 100 the beam(s) that the mobile station is able to see. The
CQI information informs the base station 100 of the quality of the
beam(s) detected by the mobile station, and the rank information
informs the base station 100 of the number of layers supported by
the current RF channel. Using the above information, the base
station 100 is able to select the beam(s) for use in transmitting
downlink data.
[0040] Beam selection also involves selecting the mode in which the
base station is to communicate downlink data with the mobile
station, where the mode can be a single input multiple output
(SIMO) mode (in which one beam is used for communicating with each
mobile station--note that multiple beams can be used for
communicating downlink data to multiple mobile stations). Another
mode of operation is a diversity mode, or SFBC mode, in which the
same data is sent in multiple beams but in different phases to
improve communication performance and cell coverage improvement.
Another possible mode is MIMO mode, in which different data is
transmitted to a mobile station simultaneously on different beams
to improve per-user throughput. Mode selection is also based on the
PMI, CQI and rank information.
[0041] Note that the beam and mode selection (406) can be performed
by a downlink scheduler (part of software 126 in FIG. 1) in the
base station 100.
[0042] Based on the selected mode and beam selection performed at
406, the base station sends (at 408) a downlink scheduling grant
message to the mobile station, where the grant message can contain
a field to indicate the mode of operation (e.g., MIMO mode, SIMO
mode, or SFBC mode). The grant message will also indicate which
codeword that the mobile station is to use. For example, the grant
message can contain a particular field that can have: (1) a first
value to indicate SIMO mode with a first codeword applied to
downlink data sent in the first beam, (2) a second value to
indicate SIMO mode with a second codeword applied to downlink data
in the second beam, (3) a third value to indicate SFBC mode to
perform transmit diversity, and (4) a fourth value to indicate MIMO
mode with a corresponding rank 2 codeword.
[0043] The above has described a technique for enabling the base
station 100 to (1) identify, for downlink data communication, the
beam that a mobile station is able to receive, and (2) select the
beam(s) that the base station is to use for transmitting downlink
data.
[0044] In preferred embodiments, to enable the base station to
determine which beam the mobile station will be using for uplink
data (from the mobile station to the base station 100), the mobile
station sends an uplink reference signal. In one example, this
uplink reference signal is referred to as a sounding reference
signal. As depicted in FIG. 5, the mobile station sends (at 502) a
sounding reference signal to the base station 100. The base station
100 then determines (at 504) whether the mobile station transmitted
the sounding reference signal in the first beam or second beam, so
that the base station can select the appropriate beam to receive
(at 506) uplink data from the mobile station.
[0045] The base station 100 can include an uplink scheduler (part
of software 126) to perform scheduling for communication of uplink
data by the mobile stations in the cell sector 108. The uplink
scheduler can perform the uplink beam selection either
independently or jointly with the downlink scheduler. When the
uplink and downlink schedulers work jointly, then the schedulers
can confirm whether or not a mobile station is in a region of a
beam. For example, if both the uplink and downlink schedulers
select a particular beam for the mobile station, then that is an
indication that the mobile station is definitely in the region
corresponding to the particular beam. However, if the uplink and
downlink schedulers select inconsistent beams for the mobile
station, then the schedulers may have to perform further analysis
to determine which of the beams is the correct one to select for
both the uplink and downlink directions. Also, during handover
between different base stations, both the uplink and downlink beam
selections have to be considered.
[0046] In some exemplary embodiments, downlink control signals can
be sent by the base station 100 as follows. For example,
synchronization signals such as a primary synchronization channel
(P-SCH) and secondary synchronization channel (S-SCH) can be sent
on both beams 104, 106 using a diversity scheme, such as a
precoding vector switching (PVS) transmit diversity scheme.
[0047] Other downlink control signals can be sent on both beams
104, 106 using SFBC diversity transmission. Examples of such other
control signals include PCFICH (physical control format indicator
channel), PHICH (physical hybrid automatic repeat request indicator
channel), and PBCH (physical channel).
[0048] Another downlink control channel is the PDCCH (physical
downlink control channel). If the number of mobile stations in a
cell sector is not large (e.g., less than some predefined
threshold), SFBC diversity transmission can be used by the base
station 100 to send the PDCCH in both beams. However, if there are
a relatively large number of mobile stations, the PDCCHs for
different mobile stations can be sent in different beams, depending
on the locations of the mobile stations. In one example, three
groups of mobile stations located in a cell sector can be
identified: (1) group 1: mobile stations in overlap region between
two beams; (2) group 2: mobile stations in first beam area; and (3)
group 3: mobile stations in second beam area. The first beam will
be used by the base station 100 to transmit PDCCHs to mobile
stations in groups 1 and 2, while the second beam will be used by
the base station 100 to transmit PDCCHs to mobile stations in
groups 1 and 3.
[0049] Another downlink control signal that can be sent using SFBC
diversity mode is the random access response message that is sent
by the base station to the mobile station in response to a random
access channel (RACH) from the mobile station. RACH is sent by the
mobile station to establish a call or other communications
session.
[0050] Although reference is made to specific exemplary downlink
channels in this discussion, it is noted that different
implementations can use different control channels.
[0051] In some exemplary embodiments, uplink control signals can be
received by the base station 100 as follows. The uplink random
access channel (RACH) is received by the base station in both beams
(so that no beam selection has to be performed). Also, the PUCCH
can also be received by the base station in both beams, or the
PUCCH can be received in either beam, where users in different
beams can be assigned the same PUCCH resources, thus increasing
PUCCH capacity (similar to uplink data).
[0052] Although reference is made to specific exemplary uplink
channels in this discussion, it is noted that different
implementations can use different control channels.
[0053] In some embodiments, for communication of uplink data or
control signaling, two mobile stations are assigned the same
resource block (same combination of time slot and subcarrier) in
two different beams. For the base station 100 to be able to
reliably receive the uplink data or control signaling in such a
scenario, the base station 100 is able to assign two orthogonal
demodulation reference signals to the mobile stations. The
demodulation reference signal sent by one mobile station will not
be shifted; however, the demodulation reference signal sent by the
other mobile station will have a half-length cyclic shift applied.
The demodulation reference signal and application of cyclic shift
is described in the 3GPP 36.211 Specification. The orthogonal
demodulation reference signals associated with the uplink data
and/or control signaling from the mobile stations will enable the
base station 100 to accurately determine the mutual RF interference
or isolation of the mobile stations in the two beams.
[0054] The orthogonal demodulation reference signal to be used by
each mobile station for uplink transmission is indicated by the
base station in the uplink scheduling grant message. The grant
message can include a parameter to indicate the cyclic shift to be
applied to the uplink demodulation reference signal for
multiuser-MIMO (MU-MIMO) mode. The parameter having a first value
indicates no cyclic shift, whereas the parameter having a second
value indicates a half length cyclic shift, to provide the
orthogonal demodulation reference signals.
[0055] Instructions of the software described above, such as
software 126 in the base station 100 of FIG. 1, can be executed on
a processor. Software can also be executed by a processor in the
mobile station 110 of FIG. 1. The processor includes
microprocessors, microcontrollers, processor modules or subsystems
(including one or more microprocessors or microcontrollers), or
other control or computing devices. A "processor" can refer to a
single component or to plural components.
[0056] Data and instructions (of the software) are stored in
respective storage devices, which are implemented as one or more
computer-readable or computer-usable storage media. The storage
media include different forms of memory including semiconductor
memory devices such as dynamic or static random access memories
(DRAMs or SRAMs), erasable and programmable read-only memories
(EPROMs), electrically erasable and programmable read-only memories
(EEPROMs) and flash memories; magnetic disks such as fixed, floppy
and removable disks; other magnetic media including tape; and
optical media such as compact disks (CDs) or digital video disks
(DVDs).
[0057] In the foregoing description, numerous details are set forth
to provide an understanding of the present invention. However, it
will be understood by those skilled in the art that the present
invention may be practiced without these details. While the
invention has been disclosed with respect to a limited number of
embodiments, those skilled in the art will appreciate numerous
modifications and variations therefrom. It is intended that the
appended claims cover such modifications and variations as fall
within the true spirit and scope of the invention.
* * * * *